Preliminary Analysis of Color Variations
of Sand Deposits in the Western Desert of Egypt
Farouk El-Baz,"^ Marie H. Siezak," and Ted A. Maxwell"
ABSTRACT
ably from place to place (ref. 1), Both mappingand handheld-camera photographs obtained on
the same mission confirmed that these color
variations abound on both regional and local
scales. It was also shown that these color variations probably reflect compositional variations of
the exposed surfaces (ref. 2). For these reasons,
an investigation was planned to document the
causes of color variations in sand deposits, which
are an important component of desert surfaces.
The Western Desert of Egypt was selected for
this study because (1) this desert was used as a test
site for the investigation of variations in color as
seen in ASTP photographs and (2) a team of
Egyptian geologists served as team members of
the ASTP Earth Observations and Photography
Experiment and were able to plan and participate
in the collection of field data.
This report must be considered as preliminary.
The number of samples reported on here is only a
fraction of the samples collected. Additional information is being gathered and analyzed by the
research team members at Ain Shams University,
Cairo, Egypt. This research is continuing under
the auspices of a joint research project between
Ain Shams University and the Smithsonian
Institution,
Astronaut observations and photographs of
color variations in the Western Desert of Egypt
are related to both iron oxide coalings on individual grains and the presence of locally derived
material in the sand deposits. The results of four
field trips, to Baharîya Oasis, Sîwa Oasis, Khârga
and Dakhla Oases, and the Great Sand Sea, enable
more detailed interpretations of colors photographed during the Apollo-Soyuz mission. The
northern region of the Western Desert has the
highest percentage of calcareous grains originating
from local limestone outcrops. Samples from the
central part of the Western Desert contain
numerous iron-rich grains originating from the
iron deposits of Baharîya and are locally enriched
in shale fragments from the Dakhla Shale. Sands
of the Great Sand Sea are relatively homogeneous,
quartz-rich deposits that vary little in percentage
of minor components. Although these results are
preliminary, they indicate the need for more
detailed field investigations of the causes of color
variations; such investigations are currently
underway.
INTRODUCTION
Visual observations made by the astronauts of
the Apollo-Soyuz Test Project (ASTP) indicated
that the colors of desert surfaces varied consider-
GENERAL SETTING
The Western Desert of Egypt is a rocky platform of sandstones and limestones that is interrupted by seven major depressions and that is
crossed by roughly north-south-trending parallel
belts of sand dunes. The largest concentration of
^National Air and Space Museum, Smithsonian
Institution.
Principal Investigator.
237
238
ASTP SUMMARY SCIENCE REPORT
dunes occupies the west-central part of the desert
and is known as the Great Sand Sea (fig, 1). The
origin of all these sand accumulations is not well
known.
The largest of the depressions, the Qattara,
measures approximately 300 km in length and
averi^es 70 km in width. The depression includes
the lowest point in the African continent, 134 m
below sea level (ref 3). Other depressions are
smaller, but they enclose the habitable Sîwa,
Faiyûm, Baharîya, Farâfra, Dakhia, and Khârga
Oases (fig, 1).
The highest areas in the Western Desert of
Egypt are in its southwestern corner and include
Gilf Kebîr Plateau and Oweinat Mountain. Most
of this region is more than 1000 m above sea level.
The central and southeastern parts of the desert
vary from 200 to 500 m above sea level, and the
northwestern and northern parts of the desert
reach a maximum elevation of 200 m (ref 3).
This setting indicates a gentle slope of the terrain from south to north. This northward lilt supports the theory that the sand deposits originated
from southern Egypt and northern Sudan. The
most likely source for the sand is the Nubian
Sandstone Formation (fig. 1). In past wetter climates, fiuvial transport by the Nile River and
other drainage systems would have been responsible for carrying sand grains from south to north.
Also, in addition to the existing Nile Delta, the ancestral delta of the Nile may have contributed
much to the accumulation of fluvial sands in the
area between the present Nile Delta and the Qattara Depression (fig. !)• (See section entitled
"Detection of a Probable Ancestral Delta of the
Nile River.") After the fiuvial deposition of the
sand grains in the north, the winds carried them
back southward in the numerous dune belts.
Western Desert. One trip was supported by the
ASTP research project, and the rest were in part
sponsored through the joint research program between Ain Shams University, Cairo, Egypt, and
the Smithsonian Institution. A brief summary of
these trips follows. (See fig. 2.)
FIELDWORK
Sîwa Oasis
The ASTP mission occurred in July 1975.
Following a preliminary review of the data, field
excursions were planned to check some of the
photographic interpretations of studied areas in
the Western Desert of Egypt. The senior author
took part in four trips that were conducted in the
The field excursion to the Sîwa Oasis (fig. 2)
was conducted in December 1976. Field checking
of color zones seen in ASTP photographs was
done on the 2Il-km-long desert road from Cairo
to Alexandria. (See section entitled "Color Zoning
in the Western Desert of Egypt.")
Baharîya Oasis
The first field trip, conducted in April 1976,
started at Cairo and followed the paved desert
road to Baharîya Oasis and El-Gedida iron mines.
The terrain from Cairo to Baharîya is basically a
rocky desert plain with few prominences.
Limestone rocks crop out approximately 90 km
southwest of Cairo and continue to the Baharîya
Depression. Any sand accumulations observed
were predominantly sand shadows in the lee of
limestone exposures.
The Qattara dunes are located midway between
Cairo and Baharîya, and are composed of dune
bundles that are very clearly exhibited on the
ASTP photographs. In most cases, these bundles
are composed of three to five longitudinal dunes
that taper and converge at their southern termini
(fig, 3). (See section entitled "Orbital Observations of Sand Distribution in the Western Desert
of Egypt.")
Iron deposits abound in the Baharîya Oasis
region and are mined at El-Gedida, where
hematite occurs as a horizontal bed of considerable thickness (fig. 4). At El-Gedida and other
areas in and around the Baharîya Depression,
hematite and limonite are exposed on the surface.
These occurrences are believed to be important
because they provide a source of sand-size iron
grains that are mixed with the sand in the Western
Desert.
•m
SAND DEPOSITS IN WESTERN DESERT
2D0km
FIGURE 1.•Map of Egypt showing the distribution or depressions (dark areas) and sand dune belts (lines of dots) in the
Western Desert. The Great Sand Sea occupies the west-central part of the desert. The Nubian Sandstone, the probable source of
most of the sand, is exposed in the southern part of the desert.
240
ASTP SUMMARY SCIENCE REPORT
'"AM
FIGURE 2.•Mosaic of fatse^:olQr Landsat ¡mages of Egypt showing color variations in the exposed rock and soil. The tracks of
field excursions in the Western Desert are shown with solid lines. The dashed lines indicate the paths of visual observation overflights at ) to 2 km altitude.
SAND DEPOSITS IN WESTERN DESERT
From Alexandria, the field team traveled along
a 300-km-long coastal road to Mersa Matmh,
where the pavement ended. From this point, the
drive followed a 300-km southwesterly track on
unpaved road to Sîwa Oasis. The exposed rock
was mostly limestone of Oligocène, Miocene, and
Pliocene age. The Miocene limestone, locally
known as the Marmarica Formation, is characterized by a reddish or pinkish color, and is
fossil i ferous, sandy, and highly brecciated (fig. 5).
This limestone may be represented in the sand
samples discussed in this paper by reddish-brown,
calcareous sand-size grains.
South and southwest of Sîwa Oasis, the northern extremities of the Great Sand Sea were investigated {fig. 1), In this region, the dunes are
noticeably smaller than those in the main part of
the Great Sand Sea farther south. Unlike the
longitudinal dunes photographed by ASTP crewmen in the southern part of the sand sea, the
dunes near Sîwa are sinuous and form short curving arcs (fig. 6(a)).
The sand color southwest of the Sîwa region
(fig. 6(a)) is light red. The reddish tint is made
more distinctive by the gray color of the
crystalline limestone that forms the rock exposures in the area (fig. 6(b)). However, the red
color is not prevalent throughout. It appears to be
most obvious on active sand surfaces, whereas inactive sand is lighter yellow in color (fig. 6(c) and
6(d)), This observation suggests the possibility of
two different sources, although in situ reddening
may also be important. The sands may have been
of mixed origin to start with, or may have been
dislodged from the rocky exposures in the area.
Following the investigation of the Stwa area
and sampling of the northern pan of the Great
Sand Sea, desert landforms were studied from an
airplane. A flight was made from Sîwa 480 km
eastward to Faiyûm Oasis and continued southward for approximately 260 km to Asyût (fig. 2).
During this fiight, the nature of the Qattara dune
belts was studied in addition to the sand dunes of
the Faiyûm area. Also, it was noticed that sand
dunes were encroaching on farmland along the
m
FIGURE 3.•ASTP pholograph of longiiudinal dune bells in
the Qattara region. Ttic southern lips of ihe dunes are migraling toward the Cairo-Baharîya Road (AST-16-1254).
western boundary of the Nile Valley from Faiyûm
to Asyût (réf. 4). This encroachment is dangerous
to the economy of Egypt, a country where the
farmland constitutes less then 4 percent of the
total area.
Khârga and Dakhia Oases
A preliminary survey of Khârga and Dakhia
Depressions was conducted in April 1977. After a
flight from Cairo to Khârga, the field investigation
was begun.
242
ASTP SUMMARY SCIENCE REPORT
FIGURE 4.•View of the El-Gedida ¡ron mine in the Bahariya Depression. Note that the red iron ore (hematite) occurs
near the surface.
FIGURE 5.•An exposure of the pink-colored, concretionary, and argillaceous limestone north of Kwa Oasis. Pencil at left center
is 13 cm long.
SAND DEPOSITS IN WESTERN DESERT
243
FIGURE 6.•Sand co!or al the northern edge of the Great Sand Sea. (a) A cluster of sinuous dunes as seen from a hill westsoulhwest of Sîwa Oasis, (b) Reddish sand ripples around a dark-gray, crystalline limestone block, (c) The windward side of a
dune that occurs on a limestone hill, approximately 20 m high, (d) The crest of the same dune showing reddish sand on the windward (right) side and a mixture of ted and gray sand on the leeward (left) side. The mixing of the two colors is apparently caused
by crosswinds on the leeward side, which form several intersecting ripples on the dune surface.
From Khârga, the field party drove northnortheast along a paved road, which was elevated
in many places to block advancing dunes. Here,
encroachment is so severe that new telephone
poles had to be attached to the original ones.
Pleistocene lacustrine deposits occur to the north
where the road becomes level with the desert surface. These outcrops are consistently streamlined
by wind erosion and are parallel in a north-south
direction. Sand tails on the leeward side of most of
these outcrops range in height from less than
0.3 m to 1,5 m. These forms are small-scale
analogs of yardangs streamlined by the action of
wind. The last stop north of Khârga was at an
enormous compound barchan. The degree of com-
paction varies significantly from the base to the
crest of this dune. Near the base of the dune, the
sand was hard and closely packed, but in other
places, our feet sank several centimeters into the
sand. The desert surface in this area is characterized by low and widely spaced sand ridges and
by a desert pavement of coarse rounded pebbles
and stones.
The trip continued west along the Ghabari
Road from Khârga to Dakhla. Just west of
Khârga, there is a field of crescentic-shaped
barchans. The first barchan, 1,3 km west of
Khârga, had completely blocked the road so that a
bypass road had to be constructed behind the
dune. Barchans are the dominant form of dunes
244
ASTP SUMMARY SCIENCE REPORT
within 20 km west of Khârga and frequently
obstruct passage.
On aerial mosaics, the barchan belt west of
Khârga is easily identified. The belt widens to the
south, and the eastern side of the dune field is
remarkably linear. Sand from the field appears to
be derived from the plateau north of the scarp
bounding the depression. These dunes are probably a continuation of the Abu Muharik dune
field. The northern scarp is characterized by a
number of parallel, linear wadis filled with sand.
A number of barchan chains emanate from these
wadis and continue to migrate southward. Fracture patterns in this area are generally east-west
and north-south, and the prevailing wind direction is north-south. Therefore, it appears that in
the Khârga area, fault and lineament trends control the distribution of sand.
Great Sand Sea
A field excursion was organized in December
1977 to investigate and sample the central part of
the Great Sand Sea and to perform detailed studies
in areas that were previously visited. This trip included visits to six oases in the Western Desert, It
started in Cairo along the desert road to Faiyûm
Oasis and then proceeded southward along the
Nile Valley to Asyut.
From Asyut, a paved desert road was followed
to Khârga Oasis and travel continued farther
south on an unpaved road to Bârîs Oasis. The
route then followed a westerly direction to Dakhla
Oasis and from there to the eastern borders of the
Great Sand Sea. From that point, the road
followed a northeasterly trend through rugged
desert terrain and numerous sand deposits toward
Baharîya Oasis, and back to Cairo (fig. 2). Upon
return, the odometers on the desert jeeps had
registered nearly 3000 km.
The investigation of sand color on this trip included comparisons made with the ASTP color
wheel. (See section entitled "Comparison of Astronaut Visual Color Observations With ASTP
Photographs.") Wherever sand samples were collected, the color of sand was compared to the
numbered color chips. In most instances, the color
of the active face of a given dune was redder than
the slip face (fig. 7).
SAMPLE ANALYSIS
Methods
Both grain size and lithologie components of 31
samples from the Western Desert of Egypt (fig. 8)
and of 1 sample from the United Arab Emirates
were analyzed. To more fully understand the color
variations seen in ASTP photographs, these colors
were compared to field and laboratory observations of sand color and texture. The bulk samples
collected varied in weight from 61 to 617 g and
averaged 305 g. Samples were split into two
halves, and one half was sieved for 15 minutes on
a Ro-Tap using standard mesh sieves at 0.250 intervals. After sieving, each size fraction was
weighed and recorded. Sediment size-frequency,
cumulative-arithmetic (fig. 9), and cumulativeprobability curves were plotted for each sample
(ref. 5). The analysis of grain composition consisted of examining the second half of the bulk
sample under a binocular microscope. In addition
to the observation of physical characteristics using
the binocular microscope, elemental analyses of
randomly selected grains were performed with a
scanning electron microscope (SEM). The SEM
has an energy dispersive system equipped with a
silicon-lithium detector and a multichannel
analyzer, which includes a display calibrated for
elements of atomic numbers 11 to 32, As a result,
it was possible to perform elemental analyses of
various grains and of specific areas or points on
the grains. Individual grains were identified according to the following scheme, and visual estimates were made of the component percentages
of each sample.
Classification Criteria
For this analysis, the components of the sand
samples were grouped under the following
classification: quartz, reddish-brown calcareous
grains, shale, white calcareous grains (dolomitic
limestone{?)), heavy minerals (glauconite,
phosphates, and hornblende(?)), ferruginous
grains (nodules, limonitic grains, and ferruginous
sandstone grains), chalk, marl, gypsum, and
calcite. The following criteria were used for identification of the components under the binocular
SAND DEPOSITS IN WESTERN DESERT
245
FIGURE 7.•The color wheel used by the ASTP astronauts in orbit is shown near the crest or a dune. The near field is part of the
redder, windward side of the dune.
14è
ASTP SUMMARY SCIENCE REPORT
200 km
FIGURE 8.•Location of numbered sand samples coHectçd by the senior author on four field trips.
247
SAND DEPOSITS IN WESTERN DESERT
1.0 .9 .8
.3
.7
.1
1 .09.08 .07
.06
Grain size, mm
FIGURE 9.•Cumulative size frequency disiribution representative of sand samples from the Western Desert. As shown by the
steepness of ihe bounding curves, mosi samples are well to tnoderately welt sorted.
microscope, supplemented by SEM analysis
where noted.
1. Quartz was identified by glossy luster,
translucence or transparence, lack of cleavage,
conchoidal fracture, lack of color, frequent frosting and yellowing, and great hardness,
2. Reddish-brown calcareous grains were identified by reddish-brown color, very low hardness,
minor crystallinity, and translucence. Supplemental SEM analysis indicates similar composition to
white calcareous grains. These two sets of grains
vary mainly in color.
3. Shale was identified by fissility and very
low hardness, and by comparison with grains
derived from an Esna Shale rock fragment, collected near Luxor.
4. White calcareous grains were identified by
white color, very low hardness, minor
crystallinity, and translucence, and by SEM
analysis.
5. Heavy minerals
a. Giauconite was identified by high
sphericity, bright- to dark-green color, very low
hardness, and high polish, and by SEM analysis.
b. Phosphates were identified by comparison of the irregular habit, black color, and interior appearance of the grains with grains derived
from a phosphate rock collected from a scarp midway between Dakhla and Khârga Oases.
c. Hornbiende(?) was identified by SEM
analysis,
6, Ferruginous grains (nodules, limonitic grains,
and ferruginous sandstone grains) were identified
by rounded habit and dark reddish-brown or
orange color. The ferruginous sandstone grains are
aggregates composed of fine angular quartz grains
within an iron oxide matrix.
7, Otalli was identified by snow-white color
and low hardness, and by SEM analysis; soft noncrystalline chalk and microcrystalline limestone
have been included under this classification,
8, Marl was identified by brown to gray color,
low hardness, calcareous composition, and lack of
crystallinity. These grains are often composed of
248
ASTP SUMMARY SCIENCE REPORT
very loosely compacted silt- and clay-size fragments.
9. Gypsum was identified by snow-white color
and extremely low hardness, by SEM analysis,
and by visual comparison with a gypsum and
clayey rock fragment collected at Sîwa Oasis,
10. Caicite grains were identified by rhombohedral cleavage, lack of color, vitreous luster,
and low hardness.
FIGURE 10.•Photomicrographs of sand grains of various
compositions and shapes, (a) Quartz grain with frosted surface; light areas in pits un the surface (A and B) are hematite,
(b) High magnification of area A showing minor erystaltinity
of iron oxides, (c) X-ray fluorescence spectrum of area B;
highest peak is located at the iron (Fe) energy level. Other
peaks are silicon (Si) and calcium (Ca). (d) Example of angular quartz grains which occur predominantly at smaller grain
sizes, (e) Highly spherical glaueonite grain. (0 Fissile shale
grain, (g) Chalk grain, (h) Marl grain.
•^
SAMPLE CHARACTERISTICS
Sample Locations
Texture and Composition
The mean grain size of most samples falls in
the range of fine sand, and the size distribution for
all samples is summarized in figure 9. As would be
expected from these wind-deposited sands, most
samples are well to moderately well sorted, and
they generally contain less than 1 percent (by
weight) silt and clay.
Because of the survey nature of this study,
many local environments were sampled, and textural characteristics for individual samples are
shown in table 1, Preliminary analyses indicate
some dependence on local environment; the
crests and windward sides of barchans generally
contain coarser grains, although there is no apparent difference in grain size on either side of
longitudinal dunes.
Although most samples are composed of more
than 50 percent quartz grains, the amount and
type of other fragments is the result of local
material. Samples from Baharîya, Khârga, and
Dakhla Oases contain the largest amounts of local
components, consisting of white and reddishbrown calcareous grains and shale. Because the individual sampling sites exert the greatest influence on components other than quartz, representative samples of exposed bedrock are used for
comparison with sand samples.
The surface texture of individual grains is predominantly a function of lithology (fig, 10). As
determined from high magnification (fig, 10(a)),
quartz grains larger than 0.20 mm diameter are
well rounded and have frosted surfaces. Iron oxides occur both within fractures of quartz grains
and in protected hollows on the grain surfaces.
Because of the regional distribution pattern of
the sand deposits, the localities are divided into
three parts: (1) the northern r^ion of the
Western Desert, including the area west of the
Nile Valley (Wâdi el Natrûn), the Qattara dunes,
and dunes southwest of the Faiyûm Oasis; (2) the
central region, which includes the oases of
Baharîya, Khârga, and Dakhla; and (3) the Great
Sand Sea, including samples obtained south of
Sîwa Oasis and southwest of Farâfra Oasis, Comparisons are made between the samples of the
Great Sand Sea with those collected near Aswan in
southern Egypt and from the eastern part of Ar
Rub' al Khâlï dunes in the United Arab Emirates.
Northern Region
IVâdi el A^airwn,•Samples at Wâdi el Natrûn
were taken from a sand sheet that shows a bright
pinkish-yellow color with a reddish tint on ASTP
photographs (ref, 2), Samples N6 and N7 were
taken from the same dune; sample N6 was collected from the more active, windward side, and
sample N7 from the slip face,* Sample N8 was located in the color zone that appears as a dusty
pinkish-gray area with mottled texture in ASTP
photographs. (See section entitled "Color Zoning
in the Western Desert of Egypt,") Field observations of this zone suggest that it has more clay and
carbonate particles than the dune from which
samples N6 and N7 were taken.
Sample numbers are referred to throughout the text, and
locations are indicated in figure S,
SAND DEPOSITS IN WESTERN DESERT
2^
350
ASTP SUMMARY SCIENCE REPORT
TABLE I.•Summary of Size Analysis Data
Sample
number
Mean grain
Size° Mz,
é (mm)
l-'nvironmeni
From Sediment Sampled
Weigh) %
sill and day
Sortinif
Skewness,"
Kurtosis. ^
Kr.
Munselt
color f
7
Wèdi El Natriiii
N6
Windward side of dune
N7
Slip lace ofdune
N8
Sand she el
1.70(0.32)6
1.79
(h)
(h)
(h)
lOYR 6/6
,40 (.75}S
8,27
(h)
(h)
(h)
lOYR 6/6
2.60 (.17)8
25.68
(h)
(h)
(h)
lOYR 6/4
Qaltara dunes
Qi
Lee side of sand dome
2,30(0.21)
0,72
0,47
+0.30
1.12
2.5Y 7/6
Q2
Windward side of sand
dome
1,86 {,28)
,05
.55
-.13
1.43
2.5Y 7/6
Q3
Lee side ofbarchan
2.23 (,22)
1,23
.48
+.20
1.16
2.5Y 7/6
Q9
Base of longitudinal dune
2,06 (.24)
,19
.85
+.07
.93
2.5Y 7/4
QIO
Sinuous segment of
longitudinal dune
1.18 (,44)
,01
.57
+.32
1.31
lOYR 7/6
Qll
Crssl of longitudinal
dune
1.78 (.30)
,41
.56
+,81
.58
2.5 Y 7/4
Fa l'y um Oasis
FI
Sand sheet
0,39 (0.78)
0.84
0.56
+0.62
2,94
2,5 Y 7/4
F3
Crest ofdune
1.89 (.28)
M
.56
+,46
1,54
2,5 Y 7/4
F4
Slope ofdune
1,80 (,29)
1.16
.54
+,53
1,45
2.5 Y 6/4
Baharîya Oasis
B4
Crescemic dune
2,57(0.17)
0.21
0,43
+0.15
0.87
2.5Y 7/4
B5
Crescentic dune
2,17 (.22)
.18
,42
+,24
1,98
2,5 Y 7/6
B6
Crescent ic dune
1.37 (.28)
.04
.43
+,29
1.36
2,5Y 7/6
^Equations for size relationships are from Folk (réf. 5).
''Graphic mean grain size:
Mz = íiti\6 + ^ÍO + ^84)/3
Cl
1 • graphic
i.- standard
. j jjdeviation:
• .•
Hnelusive
dTnclt^sivegraphlcsKewness:
Graphic kurtosis:
^95 -- ^5••
a = 084 - ^16 +. -•-.
/
4
6.6
SK, - ^'VJVJ°>^ ^SX,'.?"^
»95 - 05
K
'C " 2.44<*7.S - 1^25)
^Color of bulk sample from comparison with Munsell color chart (ref. 6),
^Median grain size (ií50) only.
'^Small sample size did not allow mote detailed analysis.
m
SAND DEPOSITS IN WESTERN DESERT
TABLL
Sample
Environment
fjtíítjbí^r
Mean K>'(¡'"
Si-e^ Mz,
<¡> (mm)
I.•Concluded
Weight %
silt 011(1 tlav
Sorliillf
7
SI(eKiicss,
SK,
Kitrlosiy^'
Mmisell
coiorJ
lOYR 6/4
Kllarfííi Oíi\s!
K6
Lee side of dune
2.51 (0.18)
1.57
0.67
+0.01
0,94
KIO
Compound barchan
2.22 (.22)
.35
.77
+.12
.80
lOYR
6/6
Kll
Compound barchan
2.20 (.22)
.41
.76
+.25
.75
lOYR
6/6
K12
Base of barchan
2.54
(.18)
,67
.56
-.04
.72
lOYR
6/6
K13
Lee side of barchan
2,03 (.25)
.39
.77
-.01
.78
lOYR
6/6
K14
Crest of arm of
barchan
2.73 (.15)
.07
.28
+.13
1,06
lOYR
6/4
K15
Cresi of barthan
2.71
(.15)
.18
.34
+.01
1,02
lOYR
6/4
K16
Windward base of
barchan
1,54 (.35)
.08
.74
+.16
.94
lOYR
6/6
Dak!}!a Oasis
D24
Base of barchan
2,50(0.18)
1.11
0.83
-0.34
1.00
lOYR
6/4
D25
Surface of barchan (dark
sand streaks)
1.46 (.37)
.12
.53
+ .07
1,10
lOYR
6/4
D26
Barchan (predominant
color)
1.71
.09
.48
+.07
1.04
lOYR
6/6
0,81
+0.75
38
lOYR
6/6
<0.01
0.45
+0,23
1.02
lOYR
6/6
(.31)
Shia Oa.\i.\
S24
Base of windward side
of dune
0.70(0,64)
<0.01
Greoi Sand Sea
GSSl
Base of sinuous longitudinal dune
0.74 (0.60)
GSS2
Arm of sinuous longitudinal dune
1.82
(.29)
.11
.61
+.04
.99
lOYR
6/6
GSS3
Crest of sinuous longitudinal dune
1,91
(.27)
.97
.39
+ .14
1.33
lOYR
6/6
0.77
+0.39
1.54
lOYR
6/6
0.39
+0.07
0.91
Asivm
A!
Sand sheet at base
of cliff
1,56(0,35)
3.32
Ar Rub' al KliSIT
UAEl
Red sands at terminus
of dune
2.61 (0.16)S
0.25
7.5YR 5/6
252
ASTP SUMMARY SCIENCE REPORT
Samples N6 and N7 are fairly clean sand. Similar to most of ihe other samples, N6 consists predominantly of quartz with minor amounts of
while calcareous grains, reddish-brown calcareous
grains, ferruginous grains (nodules and limonitic
grains) and heavy minerals {fig. 11). The heavy
minerals in all three samples have been tentatively identified as hornblende. Sample N7
differs from N6 in that it contains more heavy
minerals, no calcareous grains, and fewer
limonitic grains. The composition of these two
samples is a direct result of the local environment,
since the leeward side is better sorted compositionally and has a finer mean grain size than the
windward side.
Field observations of the color zone from
which sample N8 was taken are well substantiated
by analysis of the sample. It differs from samples
N6 and N7 by containing a higher percentage of
calcareous marl grains, minor amounts of gypsum, chalk, and calcite(?) grains, and one or two
fossils. In addition, this sample contains the
largest amount (25 percent) of silt- and clay-size
particles. The composition of this sample is likely
infiuenced by local outcrops, particularly the
"small hillocks of marly composition" that appear
in this zone, (See section entitled "Color Zoning
in the Western Desert of Egypt.")
Qattara dunes.•^The Qattara dunes are three
parallel belts of longitudinal dunes that cross the
rocky, dark-colored desert platform southwest of
the Nile Delta (figs. 1 and 2). The tips of some of
these dunes have approached the Cairo-Baharîya
Road and have even started blocking it {fig. 3).
The southern termini of these dunes are characterized by numerous complex crescentic or
sinuous dunes.
The southernmost tip is usually characterized
by a gently sloping sand dome that is perfectly
symmetrical (fig. 12). A clear color difference exists between the windward and the leeward sides
of the dome and the crescentic dunes. The windward, more active side appears redder, whereas
the leeward side is usually more gray in color.
The southern tip of the dune complex illustrated in figure 12 was sampled to see how much
compositional variation exists in the sands at the
terminal part of the dune, where mixing with
materials from the surrounding terrain is at its
maximum. Sample Ql was taken from the
leeward side of the sand dome, Q2 from the windward side of the same dome, and Q3 from the
leeward side of the first barchanlike dune at the
tip of the complex. The samples from the leeward
sides of both the dome and the barchan are finer
grained and contain more silt and clay than the
sample from the windward side. However, there is
no difference in bulk sample color between the
leeward and windward sides. This discrepancy
between field and laboratory color designation is
not unexpected because samples are from the upper few centimeters, whereas the field color
differences are due to a thin veneer of surface
sand.
Samples QI, Q2, and Q3 contain many
different components {fig. 11). Sample Ql consists predominantly of quartz and white
calcareous grains, lesser amounts of reddtshbrown calcareous grains, heavy minerals
(glauconite and hornblende(?)), and ferruginous
grains (nodules, limonitic grains, ferruginous
sandstone), and contains very low amounts of
chalk, marl, and shale.
The composition of sample Q2 is very similar
to that of Ql; the ratios of the components of both
samples are approximately the same. However,
sample Q2 does not contain any shale or marl and
has fewer ferruginous grains. Sample Q3 contains
less quartz, more white and reddish-brown
calcareous grains, and more heavy minerals than
do samples Ql and Q2. This sample also does not
include shale or marl ¡n its composition.
These three samples, however, are not characteristic of the longitudinal dunes of the Qattara
dune bundles. One of these, known as Ghard Abu
Muharik, extends from east of Baharîya Oasis in
the north to the Kharga Depression in the south.
Three samples were collected from its northern
part: Q9 from the base of the dune, QIO from the
leeward side of a sinuous dune segment, and Ql 1
from the crest of the dune.
Samples Q9, QIO, and QII contain fairly high
percentages of quartz, particularly Q9 and QIO
(fig. II). Sample Q9 includes minor amounts of
white calcareous grains, heavy minerals
(glauconite), chalk, ferruginous grains, marl, and
SAND DEPOSITS IN WESTERN DESERT
253
Wádi el Natrún
MS
N6
lOOr
a 50
• rr^f•I
Q RB
W
H
H
Fe
Fe
L r-n
Q RB
W
H
Ch M
6
C
Qattara dunes
Öl
lOOr
S 50
Q RB Sh W H
Fe Ch M
100 r
50
Sh W
H Fe Ch M
Q =
RB=
Sh"
W*
H -
quartz
reddish-brown calcareous grains
shale
white calcareous grains
heavy minerals
Fe
Ch
M
G
C
> ferruginous grains
-chalk
= marl
• gypsum
• csldte grains
FIGURE 11.•Lithologie frequency histograms indicating visual estimates of individual components in the bulk sand samples,
(Continued on following pages.)
2S4
ASTP SUMMARY SCIENCE REPORT
Fatyúm Oasis
lOOn
F4..
50-
=m
Fe Ch m
Q RB
a
W
H Fe Ch M
Q RB
-
n
W
H Fe Ch M
W
3=
H Fe Ch M
BaharIyaOasís
B4
lOOr
Ë
50
Q RBSh W
H
Fe Ch M
Q RBSh W
h Fe Ch
O RB
Siwa Oasis
Aswan
S24
Al
lïor
£í 50
L n-.-.
Q RB
W
H
Fe
Q
Sh W
Fe Ch M
Great Sand Sea
lOOr
S
GSSl
GSS2
GSS3
50-
Q
Sh
Fe Ch M
Q RB Sh
H Fe Ch M
Q RB Sh W
H Fe Ch M
C
SAND DEPOSITS IN WESTERN DESERT
^255
Khârga Oasis
m
y
K6
m
KIO
50
-Th-h-^-n
0 RB Sh W H
FeCh M
Q RB Sh W H
Fe Ch M
Q RB su w
H
193
5
Fe
M
KÏ4
W
O RB Sh W
H Fe
M
Q RBSh w
H
Fe Ch M
Q RB Sh W
tâs
100 r
H Fe Ch
»6
50
1•rn
Q RB Sh W H Fe Ch
Q RB Sh w
H
Fe
Dalthia Oasis
lÖOr
S
D24
D25
Ù26
5Û-
Q RB Sh w H
£L^
M
G
UL ru
Q RB Sh W
Fe Ch M G
L£L
Q RB Sh W
Ch M G(?l
256
ASTP SUMMARY SCIENCE REPORT
:aS:.;?:?i?Ä^^..
^.^
'^:^¡^'
.^^-r. -*
C^
^Sr^.
FIGURE 12.^View tooking north from the southern tip of the longitudinal dunes photographed by the ASTP astronauts (fig. 3).
The foreground of the photograph is occupied by a sand dome; dunes behind this dome are crescentic or complex barchan forms.
The dark areas are covered by de sert-varnished limestone and chert pebbles.
reddish-brown and green calcareous shale, which
could possibly be traced lo the variegated shales of
El-Hefhuf and Baharia Sandstone formations in
Baharîya Oasis to the north (ref. 3),
Sample QIO is fairly similar to Q9 in composition, differing mainly in the lack of shale and marl
and in the addition of a very minor quantity of
reddish-brown calcareous grains. Sample QIO also
contains slightly more white calcareous grains and
one or two ferruginous basaltic grains, possibly
derived from the dolerite intrusions of Baharîya
Oasis (ref 3).
Sample Qll differs from both samples Q9 and
QIO by containing higher percentages of white
calcareous grains and heavy minerals (mostly
glauconite), a lower percentage of quartz, and approximately twice as many ferruginous grains
(nodules, limonitic grains, and ferruginous
sandstone). This sample also does not contain any
reddish-brown calcareous grains or shale, but does
include a few calcite grains.
The percentage of white calcareous grains increases from a low value in sample Q9 to a high
value in sample Qll.
Faiyum Oasis.•Sand accumulations abound
south of the Faiyum Oasis. There are two
different types of deposits; sand sheets with
gentle swells and longitudinal dunes at the beginning of the Wadi el Ruwayân belt. Sample Fl was
taken from a sand sheet that is grayish-yellow
(21A on the color wheel (i.e., see section entitled
"Comparison of Astronaut Visual Color Observations With ASTP Photographs"), or Munsell
lOYR 7/4 (ref. 6». The color observed in the field
differs from that of the sample (see table I)
because the field observation did not include
deeper layers of sand.
Two other samples were collected from the
sand of the northern part of the Wadi el Ruwayân
dunes. These dunes are enclosed by scarps made
primarily of iight-coiored limestone with marly
and chalky intercalations. Sample F3 was taken
SAND DEPOSITS IN WESTERN DESERT
from a dune crest and sample F4 from the slope of
the same longitudinal dune. As expected from the
rapidly shifting leeward and windward sides of a
longitudinal dune, both crest and slope have approximately the same mean grain size and cannot
be distinguished on the basis of textural characteristics. They also have almost identical compositions, as illustrated by samples F3 and F4, where
the only major difference is the appearance of
calcite grains in sample F4 {fig. 11). Both samples
contain fairly high percentages of marl, presumably derived from the scarps enclosing the dunes.
Sample Fl also contains a high percentage of
locally derived chalk as well as mar!. Unlike samples F3 and F4, however, it does not contain any
white or reddish-brown calcareous grains or heavy
minerals. Basalt grains do appear in sample Fl,
however; they are probably derived from basalt
dikes north of Faiyûm (réf. 3).
Central Region
Bahanya Oasis.•Numerous dunes occur within the Baharîya Depression, Because of human activity, many of the dunes have lost their original
forms and have become either complex or subdued in shape. One sample (B4) was collected 8
km north of the village of El Bawîti and additional
samples were taken 34 km {B5) and 37 km (B6)
north of the village. Dune sand from which samples B5 and B6 were obtained appeared similar in
both localities, although both sands were lighter in
color than the sand from which sample 34 was
taken. Based on the mechanical analyses, there is
no difference in size characteristics among all
three samples. Visual estimations of the bulk sample colors, however, do not support the field observations; sample B4 is lighter in color than
either B5 or B6.
In the analysis, these three samples were found
to vary considerably from each other (fig. 11).
Sample B4 contains the lowest percentage of
quartz and the highest percentages of ferruginous
grains (nodules and ferruginous sandstone), white
calcareous grains, and chalk. This sample also includes smaller amounts of heavy minerals
(glauconite and hornblende(?)), shale, marl, and
reddish-brown calcareous grains. The iron ore of
257
Baharîya is very apparent in this sample as the
probable source of the large percentage of ferruginous grains.
Sample 85 differs from sample B4 by containing more quartz, fewer white calcareous grains,
and slightly fewer ferruginous grains and chalk. It
does not include any marl. However, the two samples do contain approximately the same amount
of grains tentatively identified as hornblende.
Sample B6 includes in its composition the highest percentage of quartz of the three samples and
the lowest percentages of white calcareous grains,
ferruginous grains, and heavy minerals. It also
contains a very small amount of hornblende(?)
and marl.
Khârga Oasis.•The Khârga Depression is
elongate in a north-south direction and measures
approximately 180 km in length. The habitable
areas in the depression lie along a major fault
(ref. 3), which is believed to have aided in bringing underground water closer to the surface.
The large longitudinal dunes that cross the
limestone plateau north of Khârga divide into
smaller dunes as they descend the northern scarp
of the depression. These smaller dunes are usually
barchans, although some longitudinal forms
develop farther to the south.
At the road marker 218 km from Asyût, a large
abandoned building is responsible for sand accumulation. Low sand mounds were found on
both the windward and leeward sides of the building and within some of the roofiess rooms. One
sample (K6) was taken from the leeward side of a
dune on the north (windward) side of the building. Farther north of Khârga, two samples (KIO
and KU) were collected from an enormous compound barchan that is approaching a star-dune
shape. Both samples of this barchan are almost
identical in size characteristics and are consistent
with the rapidly changing shape of the dune.
Just west of Khârga, samples were collected
from a field of barchans that are progressively
moving southward. One sand sample (K12) was
taken 1.3 km west of Khârga near the base of a
dune. A group of four sand samples {K13 to K16,
fig. 13) was obtained at the last barchan blocking
the road 21 km west of Khârga, Sample K13 was
taken on the leeward side at the base of the
barchan arm,K14on top of the arm, K15 from the
258
ASTP SUMMARY SCIENCE REPORT
Wind direction
Dune arm
FIGURE 13.•Schematic illustration of the method used in
sampling barchan dunes at Khat^a and Dakhia Oases. Sample
numbers are discussed in the text.
crest of the dune, and K16 from the base of the
windward slope. Laboratory analyses indicate that
the color of the two sannples from the crest is
slightly lighter than the color of those from the
base of the windward and leeward slopes (lOYR
6/4 versus lOYR 6/6; ref. 6). The sand size characteristics of this barchan, however, are consistent
with those from Natrûn and Qattara in that the
windward side is coarser grained.
All the samples from Khârga Oasis contain the
same heavy minerals (glauconite, phosphates, and
hornblende(?)) in only slightly varying amounts.
Sample K6 is composed of quartz, fairly high percentages of shale and marl, and lesser amounts of
white and reddish-brown calcareous grains, chalk,
ferruginous grains (nodules and limonitic grains),
heavy minerals, and a few fossils.
Samples KIO and Kll are very dissimilar
despite the fact that they were collected from the
same compound barchan. Sample KIO contains a
lower percentage of quartz than does sample Kll
and higher percentages of shale, heavy minerals,
ferruginous grains (limonitic grains and ferruginous sandstone), and marl. Unlike sample
Kll, sample KIO includes a small percentage of
chalk in its composition.
Of the four samples taken from the same
barchan dune (K13 to K16), the samples from the
base of the dune {K13 and K16) differ significantly from each other and also from those taken
at the crest (KM and K15). Sample K.13 (from the
leeward side of the dune) contains a higher percentage of quartz than samples K14 and K15 buta
lower percentage than K16, It also includes the
highest amount of shale, the lowest percentage of
heavy minerals, and the only marl of the four
samples. Samples K14 and K15 have virtually the
same composition. Of these four samples, K14
and K15 contain the highest percentages of white
and reddish-brown calcareous grains in equal
amounts, and heavy minerals. They also include
the lowest percentages of quartz. Sample K16 contains the lowest percentage of reddish-brown
calcareous grains and does not contain any chalk.
Individua! grains of the sand deposits in the
Khârga Oasis can possibly be traced to formations
that outcrop within the oasis and form the surrounding scarps. For example, the shale of the
samples has been specifically identified as predominantly Dakhia Shale and minor Esna Shale
by visual comparison with the grains derived from
collected rock fragments and through published
descriptions. The purple and variegated shales are
also represented. Similar techniques were used to
discover the source of other grains: the chalk
grains are presumably derived from the chalk unit
and the source of the phosphate grains would be
phosphate beds, both of which outcrop within the
oasis (ref. 3). Local outcrops therefore contribute
significantly to the iithology of the sand deposits.
Dakhia Oasis.•^Three sand samples were taken
from a barchan blocking the road that connects
Khârga and Dakhia Oases. By comparing its position on aerial photographs to its current position,
it was found that this barchan has moved
30 m in 3 years. It is an unusual duie because of
its poorly sorted sands (as observed in the field)
and its mottled colors. Sample D24 was taken
from the base of the dune where there was a predominance of calcareous sands. Sample D25 was
collected from the black sand streaks on the surface, and sample D26 was obtained from the
reddish-yellow sand representative of most of the
dune.
SAND DEPOSITS IN WESTERN DESERT
Sample D24, from the base of the barchan, has
a smaller mean grain size (2.5(it/0.18 mm) than do
samples of the surface. It also is slightly gray in
color, as is sample D25 (table I).
The microscopic analysis revealed that the
three samples are very similar, even though minor
differences do exist. All three samples contain
relatively high percentages of predominantly gray
shale, presumably derived mainly from the
Dakhla Shale and to a lesser degree from the
variegated shales and frona shales in the
phosphatic beds (ref. 3). This shale contributes
significantly to the grayer colors of samples D24
and D25, as compared to sample D26. Sample
D25, in particular, contains a high percentage of
coarse shale. Phosphate grains, probably from the
phosphate beds that outcrop in the oasis, were
found in sample D24. Sample D25 contains the
only ferruginous grains (nodules) observed in the
three samples.
2SSi
i
f
F
Great Sand Sea
Siwa Oasis.•The sample numbered S24 was
collected at the base of the reddish, windward side
of the Sfwa Oasis dune illustrated in figure 6(c). It
is a very clean sample composed of quartz, very
minor amounts of white calcareous grains, and a
few chert grains.
Grear Sana Sea (southwest of Farâ/ra).•Samples of dune sand on the eastern margin of the
Great Sand Sea were collected west of Abu Mingar, 70 km southwest of Farâfra (fig. 2). Several
gently sloping dunes occur in accumulations that
resemble those described by Bagnold as
"whaiebacks." (See section entitled "Color Zoning
in the Western Desert of Egypt.") All samples
were collected from the first line of longitudinal,
sharp-crested dunes that overlie these whaleback
dunes.
Three samples are considered in this report:
GSSI was collected from the base of a sinuous
dune, GSS2 from an arm of the same dune, and
GSS3 from the dune crest. It is significant to note
that these samples were taken from the uppermost few centimeters of sand (fig. 14). In this
area, the sand grains that form the upper layer are
redder than those beneath. The stratification is
FIGURE 14.•Layering in a 30-cm-deep trench that was dug
in dune sand of the Great Sand Sea. The surface ripples (top
hair of photograph) are made of sand that is redder than some
of the layers below the surface. The scale is 15 cm long.
similar to that of a large dune field east of Farâfra
Oasis in that alternating dark- and light-colored
layers are present in both localities.
The three samples were found to be composed
mostly of equal amounts of quartz. Differences
were observed only in the lithology of the minor
components. Reddish-brown calcareous grains
and heavy minerals were not observed in sample
GSSI, but were found in samples GSS2 and GSS3.
Sample GSSI also contains the lowest percentage
of shale and the highest percentage of chalk. Sample GSS3 is the only sample including white
calcareous grains in its composition.
260
ASTP SUMMARY SCIENCE REPORT
Aswan
For comparison with the reddish sands of the
Great Sand Sea, a sample collected just west of
Aswan (fig. 2), near the base of a cliff, was
studied. In this locality, the sand is close to its
probable source, the Nubian Sandstone (fig. 1).
However, the color of the bulk sample is the same
as most of the samples from the Western Desert
(fig. 15).
The composition of this sample does not vary
significantly from that of other samples collected
in the Western Desert. It is connposed mainly of
quartz, with minor amounts of shale, white
calcareous grains, ferruginous grains (nodules and
ferruginous sandstone), and marl. Several grains
of weathered granite(?) were found in this sample
and are presumed to be from the basement complex exposed in the nearby cliff.
Ar Rub' al Khâiï Dunes
For additional comparison with the sands of
the Great Sand Sea, one sample was collected
from another typically red sand deposit in the
United Arab Emirates. This dune sand occurs at
the terminus of the great dunes of Ar Rub' ai
K-häir (The Empty Quarter) of the Arabian Peninsula. The sample, UAEl, was collected from a
relatively low (10-m high) irregular dune mass
that was stabilized by natural vegetation south of
Abu Dhabi in the United Arab Emirates. The
quartz of this sample is very vitreous as compared
to the predominantly frosted quartz of the
Western Desert of Egypt. The reddish color is due
to extensive deposits of iron oxides on the surface
of quartz grains.
SUMMARY
Color variations of the Western Desert observed and photographed by the ASTP astronauts
can be related to minor compositional variations
within the sand deposits. Although the origin of
the sand Is not well known, the Nubian Sandstone
of southern Egypt may have provided a source for
much of the sand. As a result of four field trips
FIGURE 15.•Bulk sand samples representative of sand eolor
variations in the Western Desert, (a) Sample N6 from sand
sheet at WSdi e! Natrûn that appears bright pinkish-yellow on
ASTP photographs, (b) Qattara sample 03 froi:i the leeward
side of a barchan. (c) Sample F3 from the crest of a
longitudinal dune at Faiyûm Oasis, (d) Baharîya sample B6
collected 37 km north of El Bawîti. (e) Khârga sample K13
from the leeward side of a barchan, (f) Dakhla sample D25
showing influence of local shale fragments (Dakhla Shale) on
the sample color, (g) Sample GSS3 from a longitudinal dune in
ihe Great Sand Sea. (h) Sample Al from base of cliff in the
Aswan area.
>
made to check photointerpretations of ASTP data,
it was found that sand colors varied greatly on
both local and regional scales. Most samples are
composed of fine-sand-size grains, and are well to
moderately well sorted; and these preliminary
results also suggest a dependence on local sampling environment.
Compositional variations in both field and
laboratory studies indicate that the major color
differences result from the infiux of local material
and variation in the more r^ional occurrence of
light-colored calcareous fragments. The samples
collected from the northern and central riions of
the Western Desert are slightly lighter tn color and
less red than the samples from the Great Sand Sea
region. This difference is due primarily to the
large percentages of light-colored calcareous
grains found in the northern and central samples.
Locally, the ferruginous nodules and sandstones
at Baharîya and the predominance of shale in
Dakhla samples indicate the effect of local
material.
Although these results are preliminary, three
observations can be made on the basis of this
analysis,
1. There is a discrepancy between the color of
sand deposits noted by field investigation and that
estimated from the bulk samples. This is primarily due to the sampling of sand layers deeper
than the thin veneer that is responsible for the
color as observed from Earth orbit. More detailed
field investigations are currently being planned
that will help to account for this source of color
discrepancy,
2. The colors of bulk sand samples classified
according to the Munsell color chart vary significantly, even within the same color designation. A
SAND DEPOSITS IN WESTERN DESERT
* ^'
íífew^''?^5V|á • A!^^
'^/-V
^
^ J^^
2(51
262
ASTP SUMMARY SCIENCE REPORT
more detailed sand color chart for the Western
Desert of Egypt is being investigated to provide
more accurate ground truth for orbital data.
3. The results presented here suggest that both
dune reddening with time and the addition of
local material are important to color variations of
sand deposits. More detailed field investigations
must be made to determine the relative effect of
each of these processes before remote observations can be extended to more widespread areas.
This need is particularly important in anticipation
of the detailed color photographs that will be
available from ihe large format camera to be
flown on the Space Shuttle in the next decade.
ACKNOWLEDGMENTS
Hassan A. Eî-Etr, Geology Department, Ain
Shams University, helped to plan and conduct all
field excursions. The Geological Survey of Egypt
provided both technical expertise and vehicles for
these investigations. The Egyptian Air Force
generously provided the aircraft for observation
and transport between locations in the Western
Desert.
For mechanical analysis, the laboratories of the
Sedimentoiogical Laboratory of the Museum of
Natural History, Smithsonian Institution, were
used; the authors thank Diane Cobb for helping
with these studies; the authors are also indebted to
David George of the Geophysical Laboratory,
Carnegie Institution of Washington, for his help
in obtaining the SEM photographs and analyses.
This work was done under the Smithsonian Institution/Ain Shams University joint research
project and under NASA contact NAS9-13831.
REFERENCES
El-Baz, Farnuk; Astronaut Observations From the
Apollo-Soyui Mission. Vol. I of Smithsonian Studies in
Air and Space, Smithsonian Institution Press (Washington, D.C.), 1977.
El-Baz, Farouk: The Meaning of Desert Color in Earth
Orbital Photographs, Photogramni, Eng. & Remote
Sens., vol. 44, no. 1,1978, pp. 69-75.
Said, Rushdi: The Geology of Egypt. Elsevier Pub, Co.
(Amsterdam), 1962.
El-Baz, Farouk: Expanding Desert Creates Grim
Beauty Bui Also Threatens Crucial Cropland, Smithsonian Magazine, vol, 8, no, 3, 1977, pp, 34-41,
Folk, R. L.: Petrology of Sedimentary Rocks. Hemphill
Pub. Co, (Austin, Tex.), 1974.
Munsell Book of Color. Munsell Color Company, Inc.
(Baltimore, Md.), 1963.